A Way to Limit Risk

In a typical audit, a fixed percentage of voting districts or voting machines are checked. Choosing them at random is crucial. If discrepancies are found between the manual and electronic counts, the audit escalates to look at a greater percentage.

Interpretation of discrepancies and how to handle them can be subjective, making it important to agree upon rules and procedures in advance.

The flaw with this system is that it might miss fraud entirely if it isn’t looking in the right place. To avoid this error, a new technique is emerging as the best practice: risk-limiting audits, where a set of random ballots are pulled and compared to their digital records.

Risk-limiting post-election audits are designed to minimize the size of the audit when the outcome is correct, while with very high probability correcting the outcome, if it is incorrect, by counting all the ballots. The audit continues until there is sufficiently strong statistical evidence that the apparent outcome is right, or until all the ballots have been manually counted. There are several factors that determine the size of the audit. Two are the closeness of the race being audited and the total number of ballots cast in that race.

Next-generation voting systems should facilitate risk-limiting audits by making it easy for election officials to pull a truly random set of paper ballots for comparison with voting machine results.